Add installation instructions for Ubuntu 16.04

docs/installation.rst

@@ -140,6 +140,44 @@ The command line program should now be available:
 
    ocrmypdf --help
 
+
+Installing on Ubuntu 16.04 LTS
+------------------------------
+
+No package is currently available for Ubuntu 16.04, but you can install the dependencies manually:
+
+.. code-block:: bash
+
+   sudo apt-get update
+   sudo apt-get install \
+      unpaper \
+      ghostscript \
+      tesseract-ocr \
+      qpdf \
+      python3-pip \
+      python3-pil \
+      python3-pytest \
+      python3-reportlab \
+      python3-ruffus \
+      python3-cffi
+
+If you wish install OCRmyPDF to the system Python, then install as follows (note this installs new packages
+into your system Python, which could interfere with other programs):
+
+.. code-block:: bash
+
+   sudo pip3 install ocrmypdf
+
+If you wish to install OCRmyPDF to a virtual environment to isolate the system Python, you can
+follow these steps.
+
+.. code-block:: bash
+
+   python3 -m venv --system-site-packages venv-ocrmypdf
+   source venv-ocrmypdf/bin/activate
+   pip3 install ocrmypdf
+
+
 Installing on Ubuntu 14.04 LTS
 ------------------------------
 
@@ -157,7 +195,6 @@ Update apt-get:
 .. code-block:: bash
 
    sudo apt-get update
-   sudo apt-get upgrade
    
 Install system dependencies: